1. Technical Field
The present invention relates to an authentication technique using a digital signature, and in particular relates to a technique for enhancing the processing speed when performing authentication using an electronic certificate which has been issued by an intermediate certificate authority.
2. Related Art
As an authentication office (hereinafter termed a “CA” or “Certificate Authority”) which issues electronic certificates, there are two types: a “root CA” which is treated as a CA which can be trusted, and an “intermediate CA” which is authenticated from a root CA. Thus an intermediate CA is treated, not as a CA which is considered as being trustable just by itself alone, but as a CA which can be trusted by being verified by a root CA. In other words, a hierarchical relationship (a parent-child relationship) is established between the root CA and the intermediate CA.
Furthermore, an intermediate CA can confer authentication upon yet another intermediate CA. In this case, as seen from the root CA, the intermediate CAs constitute a plural hierarchy.
And, as for example shown in FIG. 5, signature data 210 which has been signed by the root CA is appended to an electronic certificate 200 which has been issued by the intermediate CA. Accordingly, when for example performing authentication of downloaded data 300 to which signature data 310 from an intermediate CA is appended, it is necessary first to perform authentication of the signature data 210 of the electronic certificate of the intermediate CA 200 with the electronic certificate of the root CA 100, and thereafter to perform authentication of the signature data 310 of the downloaded data 300 with the electronic certificate of the intermediate CA 200. JP-A-2005-124097 is an example of related art.